Spinal pseudoarthrosis: a complication of ankylosing spondylitis.

Fracture of the cervical spine is a recognized complication of advanced ankylosing spondylitis ( 1 ). Such fractures occur after relatively minor trauma and may appear t o be spontaneous. They are characteristically seen long after the cervical apophyseal joints have fused and vertebral osteoporosis has developed. This complication is consistent with the mechanically unstable situation that develops late in the disease: the heavy weight of the head is seated on an atrophic column of bone with numerous weak areas represented by the fused apophyseal joints and atrophic intervertebral discs. Such fractures, usually attended by neurologic complications, are often fatal. It is not widely appreciated that in this disease fractures may also occur in the lower spine. Unlike the cervical fractures, these are often clinically unrecognized but may cause pseudoarthrosis of a discovertebral joint which results in extensive bone resorption. Such lesions may have neurologic consequences, depending on the level of involvement. The following case illustrates the early and late roentgen features of this complication and documents its progressive nature over a 5-year period.